Some power switches have separate outputs through which a measurement current proportional to the load current is passed outward, which enable a user to determine the load current through the power transistor in a simple manner. The user thus has the possibility of using this information about the magnitude of the current to regulate the power switch. The user likewise has the possibility of carrying out diagnoses about the load with the aid of this information. By way of example, this information can be used to ascertain what the state of an incandescent bulb is, in order for example to notify an automobile driver that an incandescent lamp must be replaced in the near future. The power switch per se should also be reliably protected against destruction, however. By way of example, an integrated temperature sensor can regulate the power switch in such a way that the maximum permissible temperature of the power switch per se is not exceeded.
One known solution for passing a measurement current of a power semiconductor arrangement outward is shown in FIG. 2 of U.S. Pat. No. 4,885,477. The arrangement exhibits a large and a small transistor, wherein the current of the small transistor is fed to a current measuring arrangement with the aid of a PMOS transistor and a differential amplifier.
A further known possibility for passing a measurement current of a power semiconductor arrangement outward is shown in EP 1 191 693. This circuit arrangement has a switch that connects a current sensing transistor to a first or second evaluation circuit depending on a control signal.
A further known possibility for passing a measurement current of a power semiconductor arrangement outward is shown in DE 10 258 766. The latter shows a circuit arrangement with range switching for increasing the absolute magnitude of the signal at a measuring resistor, in order to increase the resolution of an analog-to-digital converter. The circuit arrangement has at least two auxiliary transistors, the signal of which is dependent on the load current, and a switching means, which connects the load paths of the auxiliary transistors individually or as a plurality in parallel.
Measuring transistors have the task of mapping as accurately as possible the current flowing through the main transistor with a specific divider ratio. In the case of an arrangement with NMOS transistors as main and measuring transistors, a differential amplifier in combination with a PMOS transistor adapts the gate-source voltage of the two transistors, which should be of the same transistor type, to one another, such that both are operated with the same current density. Local temperature, matching and other influences are not taken into account with such devices and impair the accuracy of the measurement. Measuring transistors that are therefore positioned within the main transistor considerably increase the area requirement.